Okay, here me out. I know, Adywan, you said that you will not be adding any Prequel music to ESB, and I agree that is the best way to go.
My suggestion is simple. There is an music track that was recorded for Empire back in 1980 that was edited out. The track would be played during the first part of Luke's fight with Darth Vader. What I am suggesting is to add atleast the first part of that track to that scene.
Here is a video that I edited little over two years ago that explains what I am talking about: